We ran Dan’s 3,000 cc Corvair in our yard the other day to test the static rpm of the Tennessee prop a (62 x 54) he is thinking of using for his first flights. At the bottom here we have a short video clip of the engine running.
Above, engine running on stand. It was about 40 degrees outside. The engine started with just the MA3-SPA accelerator pump for priming. Oil pressure on start and high idle (1,000 rpm) was about 65 pounds. Within 4 or 5 minutes the oil was warm enough for the pressure to come down to 50 pounds. I revved it slowly to make sure it didn’t creep back up at rpm, which it didn’t. The full static runs were about 2,525 rpm. It made excellent thrust, but Dan is in search of more rpm, as his experience with years of flying his Wicked Cleanex taught him first hand that a Corvair builds HP much faster than prop efficiency falls off, resulting in a net increase in thrust when you allow the engine to rev up. The Panther is aimed at being LSA legal, but it has a very wide potential speed envelope, and homing in on the optimal prop may take two or three tries.
Above, a slightly different angle. I hooked the battery charger to the stand because we had not charged the stands battery since CC#24 and it cranked slowly in the cold weather. I installed a NV-4500 5 speed in the red truck last month. It logged 14.4 mpg at 75 mph on the round trip to South Carolina last week. Not bad for a 3/4 ton truck with the aerodynamics of a brick, a 4 barrel carb and zero electronic controls.
My personal philosophy of unwavering allegiance to mechanical simplicity extends well beyond airplane building. Out in my hangar I have a slip roll, a bolt action .30-06 and box and pan brake that are 110, 85, and 75 years old respectively. They are all great tools, made in the US, better than you can commonly buy today. They out lived their original owners, and will likely out live me. Conversely, the computer I am typing this on, the cell phone the tv, microwave and all other electronic goods in the house, all made overseas by poor souls working in conditions I would not want for my nieces and nephews, are destined for the landfill, and I am certainly going to live long enough to drive them there myself. No consumer electronic good has ever made me as happy as a good piece of machinery. Keep this thought in mind when you are building your airplane and answer the question for yourself.
Even if your personal answer is not as polarized as mine, take comfort in the concept that your Corvair engine information comes from a source that worships reliability and simplicity. This is a far better position than taking your engine advice from a person who is fascinated with ‘high-tech’ and ‘new’, and has no understanding for nor appreciation of things long proven to work. Low tech aviation machines that will outlive you are eminently preferable to ‘new and exciting’ high tech aviation appliances that stand a good chance of dying 30 seconds before you do.
Below is a link to the film of the engine running. Notice it blew the hearing protection off my head during the run. Keep in mind that this prop is well below the level of thrust Dan is looking for.
Right now, somewhere on-line, a guy who has never built an engine, doesn’t own a plane and probably has never soloed one is writing a post that says: “Any prop less than 72″ in diameter doesn’t make any thrust at all, it is just a flywheel.” Having just stood behind such a ‘flywheel’, I beg to differ.-ww